In vehicles, so-called active engine mounts can be used to improve comfort. By means of an active engine mount, undesirable vibrations and a noise transmission to the interior of the vehicle caused thereby can be suppressed. Undesirable vibrations can occur for example upon a turn-off of one or several cylinders in an engine, which may cause the engine to run out of round. For this purpose, an actively mounted engine has a control for one or several actuators in order to counteract the vibrations of the engine with the help of the actuators in the fashion known to the person skilled in the art.
As actuators there can be utilized in particular linear actuators. These usually have a ferromagnetic stator which comprises an electrically energizable coil for generating an electromagnetic field as well as a ferromagnetic magnetic armature having at least one permanent magnet ring, which with regard to a longitudinal axis of the coil is axially movably mounted and opposes the stator. The magnetic field of the permanent magnet ring is superimposed by the electromagnetic field arising upon energizing the coil, thereby arising a linear movement of the magnetic armature as a result of electromagnetic forces.
The permanent magnet ring usually consists of several, mutually adjoining permanent magnet ring segments. On the permanent magnet ring segments attached to the magnetic armature there act, in dependence on the electrical energizing of the coil and as a result of the electromagnetic field generated thereby, loosening forces which necessitate an adhesive bonding of the permanent magnet ring segments to the magnetic armature.
Operation loads and temperature loads influence the strength of the adhesive bonded connection which may cause an embrittlement of the adhesive. This leads to an impairment of the adhesiveness of the adhesive bonded connection, so that it can come to a detachment of the permanent magnet ring segments from the magnetic armature in the course of time which in the end entails the function failure of the linear actuator.